This invention relates to the manufacture of dynamo-electric machines, and more particularly to bonding and coating the coils of dynamo-electric machine parts.
Dynamo-electric machines such as electric motors, generators, and alternators typically have an armature which rotates within a stationary stator. Both the armature and the stator typically have coils of wire wound on or otherwise applied to a ferromagnetic core. For a variety of reasons it may be desirable to solidify and/or coat these coils after they have been wound or otherwise applied. For example, solidification of armature coils may be necessary to prevent the coils from loosening under the influence of the centrifugal force produced when the armature is rotated at high speed during use of the finished dynamo-electric machine. Solidifying stator coils may reduce the adverse effects of vibration. Coating the coils of armatures and/or stators may be needed to help protect them from abrasive or corrosive environments. Solidification and/or coating may also effectively repair any defects that have developed in the insulation of the coil wire during winding of the coils.
Several techniques have been employed for solidifying and coating coils. In the case of stators, for example, the wire used to wind the coils may have a layer of bonding material over the usual insulation material. Then, after the coils have been wound, the bonding material is activated (e.g., by heat). This melts or fuses the bonding layers of adjacent coil wires together. This technique has been used for stators rather than for armatures because of a concern that the known bonding layer materials or the bonds they produce are not strong enough to withstand the centrifugal forces encountered in armatures.
The typical treatment for armature coils is to coat the coils and their leads with impregnation resins and/or gel coat resins. When being applied, impregnation resins have relatively low viscosity and are therefore capable of penetrating into the coils (e.g., by capillarity) where the resins fill the spaces between the wires forming the coils. Impregnation resins are typically applied to the coils in liquid form by dripping or bathing methods. When impregnation resins solidify, their structure is able to hold the coil wires together.
In the region between the commutator and core of an armature the coil leads may be spaced relatively far apart so that an impregnation resin may not be sufficient to anchor the leads. In that event, gel coat resin can be applied. Gel coat resins are a more viscous material capable of forming a self-supporting structure that bonds the wires together and anchors them where they have been located during winding. External coil portions which have already received impregnation resin can also receive gel coat resin. The gel coat forms a continuous, highly resistant outer layer covering the most external wires of the coils. This outer gel coat layer is particularly suitable for protecting the coils from abrasion by particles or other impurities in the air circulating in the final dynamo-electric machine.
To produce impregnation resin coatings, the dynamo-electric machine part to be coated is usually preheated. Then the resin is dripped onto the coils, typically at both ends, the resin penetrating into the coils by capillarity. After application in this way, the resin is cured in an oven. Heatless impregnation resins avoid final oven curing because they are able to gelify at room temperature. Gel coat resin application typically involves steps that are similar to those required for impregnation resins.
Returning to the use of a bonding layer on the wire used to wind stator coils, it is known to activate the material of such a layer by passing a high current for a short period of time through the wound coils in order to heat the bonding layer material by the electrical resistance of the coils. Compacting pressure may be applied to the coils to promote adhesion between the wires. To increase the abrasion resistance of coils with bonding layers, the coils may be coated with powdered resin by placing the dynamo-electric machine part in a fluidized bed of resin powder while the coil wires are still hot from activation of the bonding layer. The resin powder adheres to the still-tacky bonding layer material, thereby coating the coils. Further heating for a longer time out of the fluidized bed (e.g., in an oven) transforms the resin powder into a continuous coating on the coils. This coating renders the stator more suitable for use in an abrasive atmosphere.
All of the above-described coil bonding and coating techniques have significant shortcomings. For example, impregnation and gel coating require the handling and application of liquids which may have limited "pot life". This may mean that if the manufacturing operation has to be interrupted for any reason, the resin waiting to be used may become unusable (e.g., by hardening) and may even render the apparatus which applies it unusable. Thus it may be necessary to construct the resin application apparatus with disposable parts that are completely replaced when any significant interruption of the resin applying operation occurs. Liquid resin techniques also tend to have such other disadvantages as long production times, large manufacturing site requirements for locating coating equipment and possibly also curing equipment, and expensive coating equipment which is delicate and which requires tedious and highly expert adjustment and operation. Liquid resins may also necessitate the provision of large and expensive installations for capturing and recovering volatile components of the resins in order to avoid unacceptable pollution of the environment.
The above-described bonding layer techniques avoid many of the foregoing problems if used alone, but by itself bonding layer technology tends to produce only relatively weak bonds.
In view of the foregoing, it is an object of this invention to improve and simplify bonding and/or coating of the coils of dynamo-electric machine parts.
It is a more particular object of this invention to provide methods and apparatus for bonding and/or coating the coils of dynamo-electric machine parts, which methods and apparatus are (1) relatively compact and inexpensive, (2) easy to operate, and (3) characterized by short cycle times.
It is still another more particular object of this invention to provide methods and apparatus for bonding and/or coating the coils of dynamo-electric machine parts, which methods and apparatus reduce or eliminate the need to handle liquid resins.